h a l f b a k e r yPoint of hors d'oevre
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The Lawn Mowing Mine is a device suited to maintenance of large open lawn areas such as those found in public parks and colleges.
//Insert from [Galbinus_Caeli] anno below which does much better job of fleshing out idea than I did//
For a linear shaped charge, the cone is replaced by a V shaped
groove, and the charge is a strip of appropriate length. This makes the penetrator a narrow sheet, rather than a spike.
For this application, you are trying to slice a very low strength material, so the charge would not have to be very strong. Just enough to cause the penetrator to reach the end of the desired area. With such a weak explosion, you could easily contain the blast with a U shaped steel bar.
I can now see two varients on the Grass Cutting Mine. One for circular areas, one for rectangular.
For both of these I would envision a U shaped steel tube packed with ammonium nitrate explosives, with a V shaped groove lined with some sort of degradable material.
For rectangular areas, this bar is set up at the edge of the lawn and set off. The liner forms a flying bar that slices off the grass at the set height. The explosive residue serves as fertilizer, as does the degraded penetrator.
For larger areas, the linear bars along the edges of the lawn could be supplemented by small rings of this same linear explosive. Sort of like pop up sprinkler heads.
//End of exerpt, Thanks [galbinus]//
This would greatly reduce the cost of lawn maintenance and reduce the production of greenhouse gasses by lawn mowers.
Shaped Charges
http://en.wikipedia.../wiki/Shaped_charge
info on the technology [jhomrighaus, May 05 2006]
Bermuda Bouncing Betty
http://en.wikipedia.org/wiki/S-mine
Could also be laced with fertilizers, weed killers, and seed [normzone, Aug 06 2007]
And if it get's too tall and dry, you'll need one of these
Borate_20Bouncing_20Bettys
[normzone, Aug 25 2008]
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Annotation:
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Just don't be standing near it when it decides the grass is too long .. |
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The mine would be manually actuated by the operator. Perhaps a small platform would house the device and the operator would stand on top, or a thin biodegradable conductor could be used from a safe distance(could be integrated into the device) |
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"Honey! Why is the dog getting shorter every week!?" |
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Ideal for cone-shaped lawns, which are so hard to mow properly with a regular mower. |
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Suspect it woould turn all lawns into cone-shaped ones. |
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Also useful for weeding, tree pruning and mime clearance, I'm guessing. |
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<obligatory "When I first read this" anno> |
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When I first read this idea I thought it said Lawn Mowing Mime (thanks, DrC!) and I was having a hard time picturing how the grass was getting cut. (Perhaps the mime was going to have horizontal blades attached around the perimeter of his shoes? Can you say "mowing against the wind"?) |
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Of course, when I realized it said Lawn Mowing MINE I immediately looked around for AfroAssault :) |
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I don't have much of an understanding of explosives and the pyhsics of explosions, but I cannot conceive of how one would create a "shaped shockwave" with enough momentum to perform this function in a feasible manner. At the point of detonation, wouldn't you risk tearing out the immeditely adjacent blades of grass by their roots in order to create a blast zone of usable radius?
<mental picture - Canuck looks out across the freshly-mowed football field, slack-jawed in awe of the geometric exposed-earth polka dots now littering the once-verdant turf.> |
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This is just "a wouldn't it be cool if"--there is no hint of how to shape such a shockwave, and no evidence for the lawn-care ability of shockwaves. It's a magical mine, and dashed impractical. A window-rattling fishbone for it. |
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[Much later: fishbone withdrawn based on new posting.] |
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Shaped Charges are quite common. They were used in world war 2 to cut barbed wire, they have been used extensively in building demolitions and in antipersonel and antivehicle mines. These types of charges are also used in the cutting of steel. |
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This particular application would be a circular affair a cross section designed to focus the explosive shockwave into a narrow band. |
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As to practicality, this is the half bakery. Since when did practicallity have anything to do with half-baked ideas(it may even be that by thier very nature half baked ideas are not generally practical. |
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But isn't it the explosive force of the detonation of a shaped charge and not the shockwave that is produced that is the sole reason for creating and using a shaped charge? Or am I just farting in the wind? (Does that count as a shaped charge?) |
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To me, when a bomb goes boom there are several factors involved. You have the destructive force of the charge, ususally expressed in "pounds of TNT". I have always regarded this as a measure of how powerful the actual explosive is. You have in most cases a flash, or an emission of light consistent with the rapid combustion of expanding gases. You have the boom factor, or "how far away could you hear it go off?". This, in my opinion, is the measure of the explosion's shockwave value, and since sound waves tend to travel in all directions I still cannot see how they can be controlled so as to provide a enough concentrated energy to slice through individual blades of grass. What you will get is a grass-flattener and not a grass-cutter. |
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And a fishbone, because we are not disagreeing with the practicality of your idea, just its merits, or lack thereof. |
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I guess the closest you would get to this would be a fragmentation device. Picture a very heavy steel structure shaped like a film spool. Around the central axle is a small amount of explosive. Around that is the source of shrapnel - fine high tensile wire or small blades - which is sent out at high speed in a horizontal plane, while the spool thingy remains intact. |
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Ok, I have been going along with this because it is a bit of silly fun, but I need take a moment to be serious about shaped charges. |
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For a real discussion, go look at wikipedia. |
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A typical shaped charge is a lump of PBX with a cone shaped hole in it. The cone is lined with copper. When the explosive is set off, the copper is melted, compressed, and expelled at great speed in the direction the cone was pointed. This penetrator of hypersonic molten metal will thrust through a thickness of steel up to seven times the depth of the cone. |
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This does NOT mean that the areas not pointed to by the cone are unaffected, the explosion is still omnidirectional, just a portion of it has been redirected to blast a copper penetrator forward. |
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The charge could be contained in some sort of strong canister, to reduce the side blast, but that canister is going to be given a large recoil (basically its a rocket). |
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For a linear shaped charge, the cone is replaced by a V shaped groove, and the charge is a strip of appropriate length. This makes the penetrator a narrow sheet, rather than a spike. |
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| |
For this application, you are trying to slice a very low strength material, so the charge would not have to be very strong. Just enough to cause the penetrator to reach the end of the desired area. With such a weak explosion, you could easily contain the blast with a U shaped steel bar. |
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I can now see two varients on the Grass Cutting Mine. One for circular areas, one for rectangular. |
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For both of these I would envision a U shaped steel tube packed with ammonium nitrate explosives, with a V shaped groove lined with some sort of degradable material. |
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For rectangular areas, this bar is set up at the edge of the lawn and set off. The liner forms a flying bar that slices off the grass at the set height. The explosive residue serves as fertilizer, as does the degraded penetrator. |
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For larger areas, the linear bars along the edges of the lawn could be supplemented by small rings of this same linear explosive. Sort of like pop up sprinkler heads. |
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I can't believe I just spent that long on this. Please don't tell my bosses. |
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[Galbinus] You are right on target with that shot. That was the theory I so inadequately attempted to articulate. I have incorporated this explination into the body of the idea. |
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Somebody want to call this an urban myth so we can get the Mythbusters to try it? |
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Replace that nasty grass stuff with something else, maybe some clover and moss? No more mowing, just some weeding here and there. And for myself, no more sneezing when the freshly mown (or in this case "blown") grass particles are strewn everywhere. |
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I just noticed [GC]'s addition of a method for accomplishing this idea. I still think it's impractical, but it can be done. And, as [jhom] says, this is the Halfbakery. Fishbone withdrawn. |
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A Bermuda Bouncing Betty [link] |
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